This invention relates to a fluid jet cutting machine with a system for a contact free and selectively tactile guidance of a spacing sensor. Normally a fluid such as water or water and an abrasive can be used. In addition to the conventional thermal methods used in the cutting and separation operations of predominantly metallic plate-shaped work pieces via autogenous, oxyfuel plasma and laser cutting machines, the use of a non-thermal abrasive fluid jet cutting method is increasing worldwide.
In such a separation process, a continuous, thin jet of fluid such as water is applied and the fluid exits at a very high speed from a jet pipe at a distance of only a few millimeters from the work piece for the abrasive removal of material. Shortly before the fluid enters the jet pipe, very hard abrasives with very sharp edges and a fine grain size are added to the fluid. The fluid is under a pressure of a few thousand bar. These abrasives make it possible to treat both brittle and soft nonmetallic material, as well as almost all types of metal in an efficient manner.
One important distinction between thermal methods and fluid jet methods is that with thermal methods, the energy source, such as the gas/oxygen flame of the autogenous burner or the arc of a plasma burner, is brought adequately close to the work piece to liquefy the latter in the area where it is separated. With fluid jet cutting, there is no thermal treatment.
For fluid jet cutting, abrasive energy has its highest value in direct proximity of the outlet opening of the jet pipe. Therefore, the abrasive cutting process is most effective in this area.
It is necessary in both thermal separation methods and fluid jet cutting to maintain an optimal spacing or distance between the treating tool and the work piece.
Contact (tactile) and contactless guiding systems can be used for guiding the distance sensor to maintain the optimal distance. Guiding systems also ensure that if the position of the surface of the work piece does not remain horizontal when the tool is positioned in a vertical manner, such as when plates are supported in a position that is not completely horizontal, the clearance between the workpiece and this tool remains constant. These contactless guiding systems are used with thermal burning and laser cutting machines that automatically maintain the treatment distance during the cutting process via a trailing drive. Sliding shoes or sliding rings are used as tactile sensors. The position of these sensors in relation to the axis of treatment and direction of the work piece generates an electrical control signal that is used for trailing the treatment tool via a drive if deviations from the desired spacing should occur.
Non-contact sensors have generally been in use with thermal cutting machines for decades in the form of capacitive and inductive systems, and in the form of systems operating dependent on the arc voltage. Their electrical output signals are functions of the distance between the tool and the work piece as well.
It is not possible to use capacitive sensors in fluid jet cutting operations because these sensors will supply reliable signals only in a dry environment. Because of the treatment environment due to splash fluid, rebound, and accumulations of abrasive material, it is not possible to consider other non contact operating spacing sensor systems such as triangulation lasers and optoelectronic or ultrasound spacing or distance sensors.
Thus, in the past, fluid jet cutting machines with tactile distance (or spacing) sensors were used until now to determine the spacing or distance between the outlet opening of the jet pipe and the work piece before the drilling and cutting cycle starts. These sensors were then subsequently lifted off the work piece and not engaged further in the course of the cutting process.
Alternatively, the sensors are driven along in a sliding manner in the course of the drilling and subsequent cutting process while resting on the work piece.
With sliding tactile sensors, it is possible to carry out cutting operations with controlled regulation of the spacing both with metals and nonmetallic materials having an adequate strength. However, if the surfaces of the work pieces are sensitive, for example, such as the visible surfaces of metals or the surfaces of polished or glazed nonmetallic materials, problems arise due to scratching as a result of deposited abrasives and material removed from the surface of the work piece.
Inductive sensor systems have been used more recently in isolated fluid jet cutting operations for test purposes. These systems operate based on the principle of the retroactive effect of induced eddy current fields exerted on an inductance. These systems are not affected by fluid and steam. The rebound of the highly energetic fluid jet with the abrasive which occurs during the drilling process, but before the work piece is pierced or cut, puts extreme stress on the body of the sensor and destroys it after only a short operating time.
The inductive method cannot be used for nonmetallic materials because no eddy current fields are generated in such materials.
The present invention relates to fluid jet cutting machines for metallic work pieces that have inductive spacing sensor systems operating without being in contact with the work piece. Sensor systems of this type are designed so that the drawbacks of former tactile sensor systems in the course of the cutting process are avoided. Furthermore, this design can be adapted in a tactile manner for nonmetallic materials with the help of an additional or attachment system. Moreover, this design contains means integrated in the construction for flushing away material accumulations collecting near the jet pipe and anti-wear barrier layers for protecting the bodies of the sensors.
According to the invention, such inductive sensor systems are preferably comprised of a cylindrical main body with a short structural length. This main body is concentrically pushed over the jet pipe and either clamped to this jet pipe, or to a clamping system used for clamping on to the jet pipe. Such a clamping system consists of a metallic component with a clamping device, and a nonmetallic component associated with the inductive sensor system. Such an inductive sensor system is partly enclosed by the metallic component so that it is largely protected from mechanical forces acting on it when it is in operation.
There is also a tubular flushing guide disposed concentrically in relation to the longitudinal axis of the ring-shaped sensor. A flushing medium, which is preferably water, is guided parallel with the jet pipe and, enclosed in this jet pipe, in the direction to the end of the jet pipe. This medium directly impacts the work piece in the treatment site and is capable of flushing away material accumulations to all sides.
The flushing medium is supplied to the main body via one or more guide tubes that are connected with one another in a fixed manner. These guide tubes are arranged so that the connections of the feed hoses remain outside of the area that could be reached by the rebound or abrasives acting on it.
The electrical connection of the inductive sensor system is designed so that two or more tubes preferably leading away from the treatment plane, are protruding from the main body. At least one of these tubes has a plug connector for connecting the sensor function.
The cylindrical main body is designed so that a tactile attachment system can be concentrically pushed over it, and can then be connected with the main body by clamping or screwing it to the body.
According to the invention, the tactile attachment system comprises a preferably metallic, tubular connection body, and a guiding device that contains high rigidity versus lateral forces, but only low stiffness versus deflective forces acting in the direction of the main axis. This guide device is movable and not supported in any sliding way and only encloses the inductive sensor device. It has a ring-shaped structure and, on the side facing the work piece, it is terminated by a ring-shaped metal plate that in turn supports a replaceable sliding ring that possesses high abrasive strength. According to the invention, this guiding device has an elastic constructional means with sliding components. In addition, according to the invention, the deflective force acting in the direction parallel with the main axis can be adjusted in a simple manner, so that it can be adapted to the requirements applicable in connection with tactile spacing guidance control.